Oil well polish rod clamp for use with a rotator on a beam pumping unit

ABSTRACT

An oil well polish rod clamp includes unitary metallic cylindrical housing and a plurality of setscrews. A textured inner surface of the housing increases longitudinal gripping capacity on a rod rotated inside an oil well by a rod rotator and reciprocated by a beam pumping unit to actuate a downhole pump. The inner housing surface may include a plurality of axially short cylindrical portions with annular gaps between upper and lower portions to increase gripping pressure by reducing the contact area with the rod.

RELATED APPLICATIONS

The present invention claims priority from provisional application Ser.No. 60/993,450 filed Sep. 12, 2007.

FIELD OF THE INVENTION

The present invention relates to oil well polish rod clamps and, moreparticularly, to an oil well polish rod clamp for use with a rod rotatoron a beam pumping unit.

BACKGROUND OF THE INVENTION

The smallest oil well beam pumping units commonly used in the oilfieldare also used to de-water coal formations to allow the controlledrelease of methane gas for mine safety, and also for economic benefit asan additional fuel source. The depth of these “coal-bed methane” gaswells is typically less than 1,500 feet, making a standard size beampumping unit economically wasteful in terms of physical size, capitalexpense, and horsepower. As a consequence, the popularity of thesmallest available beam pumping units has grown substantially in thepast 10 years. The beam pumping units that are most ideal for coal-bedmethane production have only 4 inches of clearance between the two wireropes forming an assembly commonly referred to as a “bridle”.

This wireline assembly or “bridle” is the flexible power and motiontransmission component between the beam pumping unit's “horsehead”, andthe accessory “carrier bar”, which is a generally transverse cast ironor steel cross-member with a central hole to allow the polish rod topass through and be retained by a polish rod clamp. The polish rod mustsupport several thousand pounds of force during transmission of powerfrom the pumping unit and along the sucker rod string down to the pumpat the bottom of the well. To facilitate rapid and easy connection ofthe polish rod to the carrier bar during initial installation andsubsequent well servicing, a polish rod clamp is used.

Due to variations in well depth and the fact that polish rods arecommonly manufactured in lengths from 11 feet to 22 feet, this clampmust be capable of gripping anywhere along the length of the polish rod,as it is impractical to simply screw a nut on the upper threaded end ofthe polish rod for a positive load bearing connection between the polishrod and carrier bar. A nut may have to be spaced several feet above thecarrier bar, which is extremely impractical. A hinged-style polish rodclamp has been a popular method of connecting a relatively large beampumping unit to the polish rod for oil-producing wells.

Since an oil or gas well may not be drilled perfectly straight, thestring of metal sucker rods may continuously rub against the inside ofthe metal production tubing as they reciprocate. This will eventuallycause perforation of the tubing and also more commonly a separation ofthe sucker rod string hundreds of feet downhole. Both are expensivefailures to correct. The polish rod clamp includes a split metal housingwith a hinge on one side and one or more bolts on an opposing side ofthe polish rod. This design mandates that the 2-piece clamp housing be“grossly asymmetrical” instead of essentially symmetrical, i.e., it isnoticeably much longer in one direction compared to the dimension 90degrees opposite.

A discontinued variation of polish rod clamp having the trade name“No-Bolt Clamp” was symmetrical and compact enough to fit between the 4inch bridle clearance space. However, this clamp was discontinued manyyears ago because the rod gripping member utilized slip-like memberswith sharp teeth that created noticeable indentions and stress risers inthe highly stressed polish rod. When used with a rod rotator, the rotarymotion combined with the indentations and stress risers resulted inunacceptable breakage and separation of the polish rod due to fatigue.

A third type of polish rod clamp used in the oil field has the balancedesired for powering a progressive cavity pump. The sucker rod string isdriven by a rotary drive head with much clearance and no bridle aroundthe rod clamp. Instead of a hinge pin, this clamp uses bolts on oppositesides of the polish rod. The added body material on the opposing sidesmakes this design unsuitable since the clamp cannot be rotated betweenthe 4 inch wire rope spacing on bridles found on small beam pumpingunits.

Users of small beam pumping units that wish to prolong the life of thesucker rod string and tubing have had no practical way to utilize a rodrotator, since commercially available but grossly asymmetrical polishrod clamps cannot rotate between the 4 inch space between the wire ropescomprising the bridle assembly. Heretofore, these clamps accordinglycould only be used on such small pumping units without a rod rotator. Asa consequence, excessive wear and early failure of the sucker rod stringand tubing, and the resulting expensive and frequent maintenance, wasaccepted as the norm.

The disadvantages of the prior art are overcome by the presentinvention, and an improved oil well polish rod clamp is hereinafterdisclosed.

SUMMARY OF THE INVENTION

An oil well polish rod clamp includes a unitary metallic cylindricalhousing and a plurality of axially spaced set screws for pressing therod into secure engagement with the housing. A textured inner surface ofthe housing increases the longitudinal or axial gripping capacity on therod, which may be rotated inside an oil well by a rod rotator andreciprocated by a beam pumping unit to actuate a downhole pump. Thehousing may include a plurality of axially short cylindrical portionswith annular gaps between upper and lower portions to increase grippingpressure by reducing the contact area with the rod. A plurality of boltsor other force applying member may be used to force the rod intogripping engagement with the housing.

These and further features and advantages of the present invention willbecome apparent from the following detailed description, whereinreference is made to the figures in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified pictorial view illustrating the lower end of ahorsehead, a bridle between the horsehead and a carrier bar, a tubingrotator, and a polish rod clamp according to the present invention.

FIG. 2 is a cross-sectional view illustrating an inner surface of thecylindrical housing engaging the polish rod.

FIG. 3 is a cross-sectional view illustrating an alternative innersurface of a cylindrical housing.

FIG. 4 is a top view of the oil well polish rod clamp housing shown inFIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, oil well polish rod clamp 10 of the presentinvention includes a unitary and generally cylindrical housing 12 with acentral bore sized to receive a polish rod 14. FIG. 1 illustrates thelower portion of the horsehead 16 of a beam pumping unit, an accessorycarrier bar 18, which is a transverse cross member with a hole sized toallow the polish rod 14 to pass therethrough, and a rod rotator 20mounted above the carrier bar 18. For the depicted embodiment, the rodrotator has a simple handle 22 for manually rotating the rod. Bridle 24extends in the conventional manner between the horsehead and the carrierbar, and for small pumping units provides a minimum space between thebridle cables.

By providing a unitary, monolithic, donut-shaped body, the clampingmechanism associated with a split body and a hinge on one side and boltsor other clamping members on the opposing side are avoided. Also,reliable gripping engagement between the rod and the housing can be moreeasily obtained with a unitary housing rather than a split housing. Theouter circumference of the rod is generally the same as the innersurface of the housing. With a unitary housing, any differences betweenthe diameter of these surfaces can be closely controlled. With a splitbody housing, the effective diameter of the housing in engagement withthe rod is to some extent a function of the spacing between the clampedends of the housing. When the bolts, as shown in FIG. 4, engage the rodto force the rod into engagement with the housing, only a small arcuateportion of the housing is actually in engagement with the rod, and thatlimited engagement area is further decreased by the grooves discussedabove. The difference between the diameter of these engaging surfacescan be more reliably controlled with a unitary body, thereby obtaininghighly reliable gripping engagement and desired repeatability for thepolish rod clamp.

As shown in FIG. 2, the inner surface 26 of the housing 12 may provideaxially short cylindrical sections, with an upper gap and a lower gap 28between these sections. The plurality of gaps may collectively occupyapproximately 25% or more of the interior surface area of the housing,so that the area of these gaps significantly increases the area force onthe cylindrical surfaces 26.

In an alternate embodiment, as shown in FIG. 3, the inner surface of thehousing may be textured with grit-like material 30. Suitable grit-likematerials are disclosed in U.S. Pat. Nos. 4,643,740, 4,778,730,5,221,099, and 7,036,397. The presence of this grit does not result inexcessive marking of the polish rod since the grit particles themselvesare quite small in size, but does concentrate gripping forces toreliably hold the polish rod in place.

FIG. 4 depicts a top view of the housing 12, as shown in FIG. 1, andspecifically illustrates the generally cylindrical configuration of thehousing, and the circumferential positioning of the lock down bolts 32.Each of these bolts pass through the housing and are threaded in a borein the sidewall of the housing so that the bolt tip end engages rod 14.By providing upper and lower lock down bolts, and more importantly byproviding circumferentially spaced lock down bolts, the rod 14 may beeffectively forced into gripping engagement with an interior surface ofthe housing which is generally opposite the bolts, thereby tightlysecuring the polish rod in place. At least one force applying member maybe used, although at least a pair of circumferentially spaced forceapplying members, and also axially spaced force applying members, ispreferred.

In alternate embodiments, recesses other than grooves may be provided inthe inner surface, accomplishing the same purpose. Although convenientto form each groove about the entire circumference of the housinginterior surface, it is most important that recesses or grooves beprovided radially opposite the force applying members, since thegripping surfaces opposing such members (bolts) are supporting the loadby engagement. Grooves may be axially spaced as disclosed herein,although spiral grooves, vertical grooves, pockets, or other forms orrecesses alternatively may be provided on the inner surface of thehousing. A highly reliable and compact polish rod clamp is obtained byminimizing the rod/housing engagement. Also, the clamp must have asufficient height to accommodate the bolts or other force applyingmember. A plurality of grooves, as compared to one large (axially long)groove is preferred to minimize stress connection points.

Although specific embodiments of the invention have been describedherein in some detail, this has been done solely for the purposes ofexplaining the various aspects of the invention, and is not intended tolimit the scope of the invention as defined in the claims which follow.Those skilled in the art will understand that the embodiment shown anddescribed is exemplary, and various other substitutions, alterations andmodifications, including but not limited to those design alternativesspecifically discussed herein, may be made in the practice of theinvention without departing from its scope.

1. An oil well polish rod clamp, comprising: a unitary, generallycylindrical housing; the housing having a radially inner surface forengagement with a polish rod, and a plurality of grooves in the innersurface for decreasing the contact area between the rod and the housing,the inner surface engaging the rod comprising a plurality of generallyarcuate inner surfaces with recesses between the inner surfaces; and atleast one force applying member passing through the housing forengagement with the sucker rod to force the sucker rod into grippingengagement with the inner surface of the housing.
 2. A polish rod clampas defined in claim 1, wherein a plurality of recesses collectivelyoccupy 25% or more of the interior surface of the housing between anuppermost inner surface and a lowermost inner surface.
 3. A polish rodclamp as defined in claim 1, wherein the recesses on the inner surfaceare axially spaced grooves.
 4. A polish rod clamp as defined in claim 1,wherein the force applying member is one or more bolts for threadedengagement with the housing.
 5. A polish rod clamp as defined in claim1, wherein the force applying member comprises at least twocircumferentially spaced force applying members.
 6. A polish rod clampas defined in claim 5, wherein the force applying member comprises atleast two axially spaced force applying members.
 7. An oil well polishrod clamp, comprising: a unitary, generally cylindrical housing; thehousing having a radially inner surface for engagement with a polishrod, and a plurality of grooves in the inner surface for decreasing thecontact area between the rod and the housing, the inner surface engagingthe rod comprising a plurality of generally arcuate inner surfaces withrecesses between the inner surfaces; and a plurality ofcircumferentially spaced and axially spaced force applying memberspassing through the housing for engagement with the sucker rod to forcethe sucker rod into gripping engagement with the inner surface of thehousing.
 8. A polish rod clamp as defined in claim 7, wherein aplurality of recesses collectively occupy 25% or more of the interiorsurface of the housing between an uppermost inner surface and alowermost inner surface.
 9. A polish rod clamp as defined in claim 7,wherein the plurality of recesses on the inner surface are axiallyspaced grooves.
 10. A polish rod clamp as defined in claim 7, whereinthe force applying members are a plurality of bolts for threadedengagement with the housing.
 11. An oil well polish rod clamp,comprising: a unitary, generally cylindrical housing; the housing havinga radially inner surface for engagement with a polish rod, and aplurality of grooves in the inner surface for decreasing the contactarea between the rod and the housing, the inner surface engaging the rodcomprising a plurality of generally arcuate inner surfaces with recessesbetween the inner surfaces, the plurality of recesses collectivelyoccupying 25% or more of the interior surface of the housing between anuppermost inner surface and a lowermost inner surface; and a pluralityof force applying members each passing through the housing forengagement with the sucker rod to force the sucker rod into grippingengagement with the inner surface of the housing.
 12. A polish rod clampas defined in claim 11, wherein the plurality of recesses on the innersurface are axially spaced grooves.
 13. A polish rod clamp as defined inclaim 11, wherein the plurality of force applying members are bolts forthreaded engagement with the housing.
 14. A polish rod clamp as definedin claim 11, wherein the plurality of force applying members comprise atleast two circumferentially spaced force applying members.
 15. A polishrod clamp as defined in claim 14, wherein the plurality of forceapplying members comprise at least two vertically spaced force applyingmembers.